The present invention relates to a color image sensor which is movable relative to a document at least in a secondary scanning direction for reading an image on the document. It also relates to an image reading apparatus incorporating such a color image sensor.
Among prior-art color image sensors, a serial type color image sensor is known which comprises wiring boards 51, 57, an array of light emitting diodes 52, a prism 53, lenses 54, 56, a mirror 55, a semiconductor sensor 58, and a flexible cables 59, 60, as shown in FIG. 31. The light emitting diode array 52 comprises two green light emitting diodes 52G, two blue light emitting diodes 52B, and one red light emitting diode 52R, as shown in FIG. 32.
In such a prior-art serial type color image sensor, the red, the green and the blue light emitting diodes 52R, 52G, 52B of the light emitting diode array 52 are selectively turned on in succession to emit light. The light is collected by the prism 53 to irradiate an image read surface 65. The light reflected on the image read surface 65 is reduced by the lens 54, and changes its direction at the mirror 55 to be directed to the lens 56. The light is further reduced by the lens to be incident on a light receiving surface of the semiconductor sensor 58. The semiconductor sensor 58 outputs a signal corresponding to the received amount of light to the outside via the wiring board 57, the flexible cable 60, and a non-illustrated connector. Signals for driving the light emitting diode array 52 is fed from the outside via the connector, the flexible cable 60, the wiring board 57 and the flexible cable 59. The semiconductor sensor 58 is supplied with electric power and various control signals from the outside via the connector, the flexible cable 60 and the wiring board 57.
With such a prior-art serial type color image sensor, it is impossible to reliably collect light from the light emitting diode array 52 onto the image read surface 65, because the prism 53 is not satisfactorily configured on sufficient study. Further, since the red, the green and the blue light emitting diodes 52R, 52G, 52B are repetitively turned on in succession to read an image, the reading speed is low. Moreover, banding is likely to occur due to the temperature characteristics of the red light emitting diode 52R. Furthermore, in such a reduction type optical system, the lenses 54, 56 may cause image distortion, which also leads to banding. Highly accurate assembly is needed to solve this problem. Further, because of the complicated structure incorporating a large number of parts, there is a problem that the cost for the parts and assembly becomes unfavorably high.
On the other hand, among prior-art color image sensors, a contact type color image sensor is also known which includes an elongate transparent light guide member. Light from a light source enters the light guide member at an end surface thereof and is guided toward a read surface.
However, in such a prior-art contact type color image sensor, it is difficult to guide light from the light source to the read surface efficiently and evenly. To enhance the light-collecting efficiency and uniformity, a light guide member having a more complicated shape is necessary, and the assembly needs to be performed with high accuracy, which increases the parts cost.
The present invention, which has been conceived under the circumstances described above, has as an object to provide a color image sensor and an image reading apparatus which are capable of guiding light from the light source to a read surface efficiently and evenly. Another object of the present invention is to provide a serial type color image sensor and an image reading apparatus which are capable of providing a high reading speed, reducing banding, and reducing the manufacturing cost.
In accordance with a first aspect of the present invention, there is provided a color image sensor movable relative to a document at least in a secondary scanning direction for reading an image on the document comprising: a white light emitting diode for emitting white light; a generally sector-shaped prism having a shorter edge surface facing a white light emitting surface of the white light emitting diode, a longer edge surface facing a read surface of the document, a front and a rear surfaces spaced from each other in the thickness direction of the prism, the front and rear surfaces being so curved as to collect white light emitted from the white light emitting diode onto the read surface of the document; a semiconductor color sensor including a plurality of red light receiving elements, a plurality of blue light receiving elements and a plurality of green light receiving elements for receiving light reflected on the read surface and for simultaneously outputting red, blue and green image signals; and a lens means for forming a non-magnified erect image on the light receiving elements of the semiconductor color sensor in accordance with light reflected on the read surface.
According to a preferred embodiment, a single white light emitting diode, a single prism and a single semiconductor color sensor are provided, and the color image sensor is movable relative to the document both in a primary scanning direction and the secondary scanning direction for reading the image on the document.
Preferably, the lens means may comprise a rod lens array.
Preferably, the lens means may comprise a pair of convex lens arrays disposed in series in an optical axis direction.
Preferably, the white light emitting diode and the semiconductor color sensor may be mounted on a common wiring board.
Preferably, the color image sensor may further comprise a housing for accommodating the prism and the lens means, wherein the housing has a pair of first counterpart surfaces which face edge surfaces of the wiring board, respectively, and a pair of second counterpart surfaces which face edge surfaces of the white light emitting diode, respectively. A total spacing between the second counterpart surfaces of the housing and the edge surfaces of the white light emitting diode may be set smaller than a total spacing between the first counterpart surfaces of the housing and the edge surfaces of the wiring board. The white light emitting diode may be positionally limited by the second counterpart surfaces, thereby positioning the wiring board.
Preferably, the color image sensor may further comprise a transparent cover member provided between the read surface and each of the prism and the lens means, wherein the cover member may be integrally formed on the prism.
Preferably, the red light receiving elements, the blue light receiving elements and the green light receiving elements of the semiconductor color sensor may be respectively arranged at a predetermined pitch in a row extending in a primary scanning direction. The rows of red, blue and green light receiving elements may be spaced from each other at a predetermined pitch in the secondary scanning direction.
Preferably, the pitch between the rows of red, blue and green light receiving elements in the secondary scanning direction is twice the pitch between the light receiving elements of a same color in the primary scanning direction.
According to a second aspect of the present invention, there is provided an image reading apparatus incorporating the above-described color image sensor, wherein the red light receiving elements, the blue light receiving elements and the green light receiving elements of the semiconductor color sensor are respectively arranged at a first pitch in a row extending in the primary scanning direction, the rows of red, blue and green light receiving elements are spaced from each other at a predetermined pitch in the secondary scanning direction; the image reading apparatus comprising: a secondary scanning direction driving section for reciprocally moving the document and the color image sensor relative to each other at a second pitch in the secondary scanning direction; a primary scanning direction driving section for moving the document and the color image sensor relative to each other at a third pitch in the primary scanning direction after every forward movement and after every reverse movement, respectively, by the secondary scanning direction driving section; and an image processing section for combining the image signals of the different colors from the semiconductor color sensor into a set of red, blue, and green image signals for each identical pixel while disregarding a line of image signals which do not contain image signals of either color.
Preferably, the second pitch maybe equal to the first pitch, and the pitch between the rows of red, blue and green light receiving elements in the secondary scanning direction may be twice the first pitch.
According to a third aspect of the present invention, there is provided a color image sensor movable relative to a document both in a primary scanning direction and a secondary scanning direction for reading an image on the document comprising: a white light emitting diode for emitting white light; a semiconductor color sensor including a plurality of red light receiving elements, a plurality of blue light receiving elements and a plurality of green light receiving elements for receiving light reflected on the document and for simultaneously outputting red, blue and green image signals; and a lens means for forming a non-magnified erect image on the light receiving elements of the semiconductor color sensor in accordance with light reflected on the document.
Preferably, a single white light emitting diode may be provided.
Preferably, the red light receiving elements, the blue light receiving elements and the green light receiving elements of the semiconductor color sensor may be respectively arranged at a predetermined pitch in a row extending in a primary scanning direction. The rows of red, blue and green light receiving elements may be spaced from each other at a predetermined pitch in the secondary scanning direction.
Preferably, the pitch between the rows of red, blue and green light receiving elements in the secondary scanning direction may be twice the pitch between the light receiving elements of a same color in the primary scanning direction.
Preferably, the lens means may comprise a rod lens array.
Preferably, the lens means may comprise two convex lens arrays disposed in series in an optical axis direction.
Preferably, the color image sensor may further comprise a housing for accommodating the white light emitting diode, the semiconductor color sensor and the lens means; wherein the housing may be formed with a light guide hole for guiding white light emitted from the white light emitting diode to the document, and at least wall surfaces of the housing defining the light guide hole may be white.
Preferably, the housing may be entirely white. Preferably, the white light emitting diode and the semiconductor color sensor may be mounted on a common wiring board.
Preferably, the color image sensor may further comprise a clip type connecting means mounted on the wiring board, wherein the connecting means may supply electric power from outside the wiring board to the white light emitting diode while feeding image signals of each color from the semiconductor color sensor to outside the wiring board.
Preferably, the connecting means may comprise a clip pin.
Preferably, the connecting means may comprise a clip connector.
According to a fourth aspect of the present invention, there is provided an image reading apparatus incorporating the above-described color image sensor, wherein the red light receiving elements, the blue light receiving elements and the green light receiving elements of the semiconductor color sensor are respectively arranged at a first pitch in a row extending in the primary scanning direction, the rows of red, blue and green light receiving elements are spaced from each other at a predetermined pitch in the secondary scanning direction; the image reading apparatus comprising: a secondary scanning direction driving section for reciprocally moving the document and the color image sensor relative to each other at a second pitch in the secondary scanning direction; a primary scanning direction driving section for moving the document and the color image sensor relative to each other at a third pitch in the primary scanning direction after every forward movement and after every reverse movement, respectively, by the secondary scanning direction driving section; and an image processing section for combining the image signals of the different colors from the semiconductor color sensor into a set of red, blue, and green image signals for each identical pixel while disregarding a line of image signals which do not contain image signals of either color.
Preferably, the second pitch may be equal to the first pitch, and the pitch between the rows of red, blue and green light receiving elements in the secondary scanning direction may be twice the first pitch.
According to the present invention, the prism is generally sector-shaped with the shorter edge facing the white light emitting surface of the white light emitting diode, and the longer edge facing the read surface. Further, the front and the rear surfaces spaced in the thickness direction of the prism are so curved as to collect white light emitted from the white light emitting diode onto the read surface. Therefore, it is possible to collect light from the light emitting diode at the read surface efficiently and evenly.
Further, according to the present invention, a semiconductor color sensor is provided which includes a white light emitting diode for emitting white light, a plurality of red light receiving elements, a plurality of blue light receiving elements and a plurality of green light receiving elements for receiving light reflected on the document and for simultaneously outputting red, blue and green image signals. Therefore, it is possible to obtain red, blue and green image signals simultaneously by lighting the white light emitting diode, which increases the reading speed. Further, since a white light emitting diode is used, it is possible to avoid banding which may otherwise caused due to the temperature characteristics of a red light emitting diode. Furthermore, since a reduction type optical system is not used, banding due to image distortion by the lens can be reliably reduced without the need for highly accurate assembly. Moreover, because of the simple structure and small number of parts, it is possible to reduce the manufacturing cost.
Other features and advantages of the present invention will become clearer from the description of embodiments given below with reference to the accompanying drawings.